The present invention relates to a dryer section of a machine for the production of a fibrous web, for instance a paper web.
The dryer section comprises a plurality of dryer groups arranged one after another in a path of the web through the dryer section; each dryer group comprising at least one, and more usually a plurality of drying cylinders arranged in sequence of the path of the web. Typically, there is an endless porous support belt that passes the web around successive drying cylinders. Generally, each drying cylinder is followed by a reversing roll for guiding the support belt, e.g. onto the next drying cylinder in the path of the web through the drying section. The support belt partially wraps around each of the drying cylinders. The web is supported on the support belt so that the web directly contacts the drying cylinders, while the support belt directly contacts the reversing rolls. Typically, the reversing rolls are suction rolls.
The web should leave the drying cylinder with the support belt. As described below, appropriate suction means are provided for accomplishing that result.
The invention also relates to a dryer section with inclined rows of drying cylinders for shortening the structural length of the dryer section. In that case, the dryer cylinders are arranged in a plurality of rows and the web travel pathway, guided by the respective web support belts in the dryer groups is such that the web alternately passes down one row and up the next row through the dryer groups.
Such dryer section forms the object of U.S. Pat. No. 5,050,310. A traditional drying section has only horizontal rows of drying cylinders. In the just mentioned patent, it was attempted to shorten the structural length of the dryer section by arranging the dryer cylinders in predominantly vertical rows. Individual dryer cylinders are shifted out of the vertical row so as to produce a row which, although it is not linear, is inclined to the vertical. A forwardly inclined row is followed by a rearwardly inclined row so that the cylinder rows succeed each other in the manner of a zig-zag line.
The object of U.S. Pat. No. 5,177,880 is to further develop the proposed dryer section so that it can be installed easily and can be accessible in operation and, furthermore, so that the machine frames of the section are formed of simple parts.
This object is achieved by the following primary feature: The rows of dryer cylinders being oriented so that successive rows of dryer cylinders alternate, with one row being inclined from the vertical rearwardly and upstream in the path of the web through the dryer section and the next row being inclined from the vertical forwardly and downstream in the path of the web through the dryer section. Two adjacent oppositely inclined rows incline toward each other, with one pair of rows inclining toward each other vertically downward and the next pair or rows inclining toward each other vertically upward. Two rows inclined toward each other define a generally V-shaped double row.
Instead of there being a single dryer cylinder generally at the apex of the V, particularly in order to enable removal of break paper, the end or final dryer cylinder off of which the web comes from the upstream row and the start or first dryer cylinder in the next row in the V-shaped double row are arranged horizontally alongside each other.
It is therefore preferred that all, or at least nearly all, of the rows of cylinders have the same number of cylinders, and preferably three cylinders per row. Providing three cylinders Per row is already known from U.S. Pat. No. 4,744,156. In that case, however, all of the rows of cylinder are inclined in the same direction, namely all are inclined toward the rear or upstream or all toward the front or downstream. This has the disadvantage that the spaces between two adjacent rows of cylinders are very narrow. In contrast to this known arrangement, the cylinders of the invention are arranged along a "rack profile". This retains the previously relatively large spaces between the rows of cylinders, which enables the temporary removal and reinstallation of the an individual dryer cylinder. Furthermore, this provides space for known drying air blast and suction boxes at least at some of the reversing rolls, similarly to U.S. application Ser. No. 321,761, now U.S. Pat. No. 4,986,009, which is mentioned in U.S. application Ser. No. 07/467,788, filed Jan. 19, 1990. For showing of such features, the disclosures of these U.S. specifications are incorporated herein by reference.
Although three dryer cylinders in each row, which has a plurality of dryer cylinders, is preferred, there may be as few as two or as many as four in a multi-cylinder row. The rows of dryer cylinders usually have about the same number of dryer cylinders. At least one of the dryer groups has at least two rows. At least one of the dryer groups may have only a single row. The dryer group has a single supporting belt which passes over all of the dryer in the dryers group. Two rows forming a V-shaped double row may be in a single dryer group or may be respective parts of two successive dryer groups.
A framework of beams and posts supports the rows of dryer cylinders. Preferably, that framework includes beams and posts that supports the dryer cylinders of two rows forming a V and particularly a V with its apex downward, wherein the lower cylinders are supported at a first lower plane, the upper cylinders of the two rows are supported at an upper plane and if there are central dryer cylinders between the support and lower dryer cylinders, the central cylinders are supported at a central plane. Appropriate means are provided for either articulating some of the beams or removing part of them to gain access to the particular dryer cylinders for easy replacement.
As appropriate, blast scrapers may be provided at the dryer cylinders, and air blast boxes at some of the reversing rolls.
A partition wall may extend between the rows of a double row of dryer cylinders and that partition wall may include channels for feeding drying air and/or be provided adjacent dryer cylinders for feeding drying air to the supporting belt and into the pocket between adjacent dryer cylinders.